Technical Field
The present disclosure relates to an electrophotographic photoconductor, and an image forming apparatus and a process cartridge using the electrophotographic photoconductor.
Description of the Related Art
In an image forming method performed by an electrophotographic image forming apparatus, an image is formed by exposing an electrophotographic photoconductor (hereinafter may be referred to as “photoconductor”, “electrostatic latent image bearer”, or “latent image bearer”) to the processes of charging, irradiation, developing, transfer, etc. Nowadays, organic photoconductors (OPC) that use organic materials are widely used as the electrophotographic photoconductor in terms of their flexibility, thermal stability, and film formation property.
Among various types of organic photoconductors, function-separated multi-layer photoconductors are now the mainstream, which have a charge generation layer containing a charge generation material and a charge transport layer containing a charge transport material each stacked on a support. The charge generation layer and charge transport layer serve as photosensitive layers. In particular, a number of negatively-chargeable photoconductors have been proposed which have a charge generation layer containing an organic pigment as a charge generation material and a charge transport layer containing an organic low-molecular-weight compound as a charge transport material. A technique of providing an undercoat layer between a support and a photosensitive layer has also been proposed for the purpose of suppressing charge injection from the support.
The organic photoconductors are required to have much higher durability and stability in accordance with the rapid progress of image forming apparatus technologies in terms of colorization, speeding up, and higher definition. On the other hand, through repeated exposure to the charging and neutralization processes in electrophotography, the organic materials contained in the organic photoconductor will gradually denature to cause deterioration in electrophotographic properties. As a result, charge trapping or charge property change will occur in the layers.
Such deterioration in electrophotographic properties caused by repeated use of the organic photoconductor largely affects the quality of the output images. For example, decrease in image density, background fog, residual image, and/or non-homogeneous image after continuous printing may be caused.
One factor that causes such deterioration in electrophotographic properties is considered deterioration of the undercoat layer. Generally, the undercoat layer is required to have the following two functions constantly: a function of preventing charge injection from the support into the photosensitive layer (hereinafter “charge injection prevention function”) and a function of transporting charges generated in the photosensitive layer to the support (hereinafter “charge transport function”). The charge injection prevention function and charge transport function have a large influence on charging characteristics and optical attenuation characteristics of the photoconductor, respectively. Because these two functions are contradictory, it is very difficult to achieve a good balance therebetween.